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SN74LVC16244A: What is the behavior when one SN74LVC16244 is active and connected to another SN74LVC16244 without power?

Adam Torma
Mastermind 45575 points
Part Number: SN74LVC16244A

e2e, 

I'm using SN74LVC16244 in switch product for signal hotswap purpose.

There are two separate boards, Board A and Board B has connection from SN74LVC16244.(two board has some ground)

 

A board, output is high, and B board’s power VDD3.3V_B drop, we can see VDD3.3V_B has 0.75V to ground, and A board’s input pin is clamp to low.

 

A board output pin is low when B board power VDD3.3V_B drop, then A board pin are normal, VDD3.3V_B is normal 0V, and A board’s input pin is high.

Could you please help analyze when A board is active and B board is power loss, how to impact SN74LVC16244’s behavior? Thanks.

Adam 

  • 0
    TI__Guru* 97046 points

    Hello,

    It sounds like you need to know what happens in the case that one device is outputting 3.3V, while the other device has a very low supply voltage (0.75V).

    Inputs won't be affected by voltages larger than the supply for the SN74LVC16244A, however outputs should not have voltages larger than the supply applied when they are active.

    The operation of the SN74LVC16244A is not defined for voltages between 0V and 1.65V, so I can't be sure of the output state in the case of 0.75V supply.  If the supply were held at 0V, then we could use the Ioff definition provided in the datasheet, which is that all pins are in the high impedance state:

    You could also force the OE\ pins to VCC  with a pull-up resistor so that outputs are disabled when power it removed, which eliminates the unknown state.